add jpa dependency

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1484744 13f79535-47bb-0310-9956-ffa450edef68
add @Entity annotation to ease cassandra impl

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1484745 13f79535-47bb-0310-9956-ffa450edef68